Air distribution plenum with silencer for head enclosures

ABSTRACT

A plenum adapted to be mounted in a head protective hood for distributing respiration air to the interior of the hood. The plenum is formed by an air distribution tube that has a plurality of air jet openings in the wall thereof and spaced along the tube to achieve a desired distribution. Fabric in the form of a sleeve disposed within the tube and overlying the air jet openings in the tube so as to break up the airflow through the jet openings to reduce noise level. A fabric sleeve disposed on the outer surface of the tube for breaking up airstreams exiting the jet openings in the tube. Structure for supporting the fabric sleeves in their respective positions.

, United States Patent [72] Inventors Herbert A. Rmchke 5 Referen e c d Gmbns M San both f UNITED STATES PATENTS I 692,211 1/1902 Reenstiema 181/55 821,828 5/1906 Phelps 181/60 X A.PPL 2,577,607 12/1951 Conley 181/36 ux [22] Filed June 1, 1970 3,036,656 5/1962 Ange1ery.. 181/56 X {45] Patented Aug. 24, 1971 Assign ED B u C may 3,208,551 9/1965 Carls 181/60X Sa H can. 3,339,668 9/ 1967 Trainor 181/60 X Primary Examiner-Robert S. Ward, Jr. Attorney-Townsend and Townsend ABSTRACT: A plenum adapted to be mounted in a head protective hood for distributing respiration air to the interior of [54] WITH SILENCE! the hood. The plenum is formed by an air distribution tube 1 l C 4 D that has a plurality of air jet openings in the wall thereof and "wing m spaced alon the tube to achieve a desired distributionv Fabric I E [52] US. Cl 181/36 R, in the form of a sleeve disposed within the tube and overlying I 181/36 B, 181/55, 181/56, 181/60 the air jet openings in the tube so as to break up the airflow [51] Int. CL A42b 3/00, through the jet openings to reduce noise level. A fabric sleeve F01n 1/08,F01n 7/08 disposed on the outer surface of the tube for breaking up [50] Field oiSearch 181/36 R, airstreams exiting the jet openings in the tube. Structure for supporting the fabric sleeves in their respective positions.

PATENTED AUG24 IBYI F fg. 4

M/VE/VTOR HERBERT ,4- RASCHKE 5) 1 ATTORNEYS AIR DISTRIBUTION PLENUM WITI-I SILENCER FOR I HEAD ENCLOSURES This invention relates to an air distribution plenum for'head enclosures of the type worn by sandblasters and more particularly to an air distribution plenum that distributes adequate respiration air without producing an excessive noise level.

Health and safety requirements dictate that those working in atmospheres having deleterious airborne substances wear a head enclosing hood to the interior of which pure respiration air is supplied. Supply of air to the enclosure is typically achieved by delivering the air through a tube which has one or more openings through which air egresses to the interior volume of the enclosure. Unless special precautions are taken,

such air as it exits the tube produces a whistlelike sound at an audible level that is bothersome and fatiguing to the wearer of the enclosure. A specific maximum noise level, as specified in regulations promulgated under the aegis of the UnitedStates Secretary. of Labor, is .90 decibels (db.), such regulations prescribing that those exposed to a noise level in excess of 90 db. must be given frequent rest periods to avoid permanent adverse effects from such excessive noise level.

An object of the present invention is to provide an air distribution plenum for head enclosures that avoids production of noise levels in excess of 90 db. In fact the noise level produced when employing a preferred embodiment of the present invention limits the noise level to well under 80 db., a levelthat is not bothersome or hazardous to the user of an enclosure ,employing the invention.

A satisfactory form of the invention includes a hollow semirigid plastic tube mounted within a head protective enclothe region thereof where the air jet openings are formed, is

provided with a fabric sleeve, the individual fibers of which are spaced from one another to form pores that have a size much less than-the diameter of the air openings. Upstream of the region where the air openings are formed in the tube, the fabric sleeve is secured within the tube so that air passing through the tube must flow through the spaces between the fibers of the sleeve in order to reach the air outlet openings in thejtube wall. Such structure is thought to break up the flow of air to such a degree that the noise level is materially reduced. Also included in the preferred embodiment of the present invention is a second fabric sleeve secured to the exterior surface of the tube for contributing to accomplishment of the same purpose, as the air exits the openings in the tube wall.

Another object is to provide an air distribution plenum that affords the above-described advantages in a simple and inexpensive structure. Contributing to the achievement of this object is the provision of a flanged cylindric insert that fits into the air distribution tube at the inlet end thereof. The inner fabric sleeve is held captive between the tube all and the insert by compressive forces arising as the insert is pressed into the end of the tube. Not only does the insert fix the inlet end of the sleeve but it assures that all air entering the device will pass through the pores of the sleeve before the air escapes through the jet openings in the tube wall.

The foregoing together with other objects, features and advantages of the invention will be more apparent after referring to the following specification and accompanying drawing in 'which:

FIG. 4 is a view of the end of the plenum opposite the inlet end with portions broken away to reveal certain internal details of construction.

Referring more particularly to the drawing, reference numeral 12 indicates an air distribution plenum according to the present invention that is intended for installation in a head protective enclosure. Such enclosure is not further shown or described, since it forms no part of the invention. The plenum is formed by a relatively rigid plastic air distribution tube 14 to which is connected an air delivery tube 16 the remote end of which is supplied with filtered air from a compressor and filter system not shown. A joint 17 is provided for connecting air delivery tube 16 to air distribution tube 14. The end of air distribution tube 14 remote from connection 17 is closed, as at 18, and the walls of tube 14 are provided with a series of air jet openings 20 so that air supplied to the interior of the air distribution tube is distributed through openings 20. Air plenum 12 is typically installed in an enclosure above the face of the wearer with air jet openings 20 directed downward so that a stream of fresh air is directed over the face of the wearer. Mounted within air distribution tube 14 is a'fabric sleeve 22 that overlies the interior of air jet openings 20 so as to break substantially devoid of sharp edges.

For securing inner sleeve 22 within tube 14 and assuring that air supplied to the tube is directed to the interior of the sleeve, there is included an insert fitting 24 formed by a generally cylindric portion 26 and an annular flange 28. The outer diameter of cylindrical portion 26 is less than the inner diameter of air distribution tube 14, and the outer diameter of flange 28 is greater than such inner diameter so that axial movement of insert 24 is limited by the flange. Moreover, the external surface of cylindric portion 26 is provided with a slight taper to expedite assembly of the air plenum. As shown in FIG.2, the outer diameter of cylindric portion 26 is sufficient to admit sleeve 22 between the insert and tube 14 but is large enough to snugly engage the sleeve to prevent movement thereof. Insert 24 is provided with a central opening 30 to admit air from air delivery tube 16 to the interior of sleeve 22. For joining air delivery tube 16 to air distribution tube 14, a tapered annulus 32 of conventional form is provided in circumscribing relation to the air distribution tube and an interiorly threaded nut 34 has a surface complemental to the tapered surface of annulus 32 so that axial force on the nut compresses the annulus to form an airtight seal. The end of air delivery tube 16 is male-threaded at 36 to engage the threads on nut 34 thereby completing the connection. It will be noted that the end of air delivery tube 16 can be formed with a flat face to urge insert 24 into its operative position within air distribution tube 14. Thus, joint 17 connects the air delivery tube to the air distribution tube, establishes air flow therebetween, and assists in retaining the inlet end of sleeve 22 in its operative position.

Sleeve 22 at the end thereof remote from joint 17 is folded back over itself as indicated at 38 in FIG. 4. The amount of the sleeve that is folded back on itself is preferably short enough that the last air jet opening 20b is not obstructed by more than a single layer of the material of which the sleeve is formed. The folded-over length must be sufficient, however, to avoid escape of air through the longitudinal end of the sleeve and to support the end of the sleeve adjacent end 18 of air distribution tube 14.

It has been found that sleeve 22 installed as described above is suflicient to reduce the noise level produced by air passing through jet openings 20 to a level below db. A further reduction is achieved, however, by securing to the outer sur face of air distribution tube 14 an outer fabric sleeve 40. Outer sleeve 40 is secured in place by flexible adhesive-bearing tape 42 and 44 which is wrapped around the ends of sleeve 40 outside of the extreme jet openings a and 20b. Outer tube 40 is of a character and function similar to inner sleeve 22 in that the size and texture of the individual threads that constitute the outer sleeve are sufficient to break up the airstream that egresses from each air jet opening 20 whereby noise is reduced or eliminated.

Certain techniques of assembly have been developed which contribute to the advantageous characteristics of the present invention. Installation of inner sleeve 22 has been successfully achieved by first cutting the sleeve to proper length and then inserting into the inner opening of the sleeve a relatively rigid rod. The folded back portion 38 of the sleeve is formed by folding the sleeve back over the end of the rod and then the sleeve and rod are inserted into air distribution tube 14. When the rod bottoms against end 18 of tube 14, the rod can be removed without dislodging the inner sleeve. Thereafter, the opposite end of the sleeve is folded over the end of tube 14 adjacent joint 17, and insert 24 is inserted to retain firmly the inner sleeve in place. For installing the outer sleeve, it is preferred that the sleeve be moved into place in circumscribing relation to air distribution tube 14 after which one end, for example the end indicated in FIG. 4, is secured by wrapping tape 42 therearound. As shown, the tape. overlaps the end of the sleeve so as to achieve adherence to the surface of tube 14. Then the sleeve 40 is stretched axially thereof until it is in tightly embracing relation to the exterior surface of air distribution tube 14 whereupon the opposite end is fixed by wrapping tape 44 therearound.

For exemplifying without limiting the present invention, the following dimensions of one satisfactory embodiment of the invention aredisclosed. Air distribution tube l4'is formed of plastic tubing having a nominal inside diameter of one fourth .inch'and an outside diameter of three-eighths inch. Air jet openings. 20 are 50 in number and have a l l 16-inch diameter spaced apart on centers by a distance of three-sixteenths inch. The length of air distribution tube 14 is sufiicient to extend around at least the front region of the head enclosure. Inner sleeve 22 and outer sleeve 40 are formed of nominal %-inch inside diameter cotton sleeving. insert 24 has an outside diameter suitable for compressing sleeve 22 and securing it against movement and inner diameter of air passage 30 in the insert is approximately three-sixteenths inch.

In using air plenum constructed according to the present invention, the air plenum is installed in a helmet or like head protective enclosure by suitable clamps or the like at a position preferably located above the face of the wearer of the enclosure. The plenum is oriented so that air jet openings 20 are directed in a downward direction. Air delivery tube 16 is passed through a suitable opening in the enclosure and is con-' nected by way of a hose or the like to a suitable source of filtered air. The air supply is turned on to a level suitable to afford adequate ventilation and respiration to the user of the device and it has been found that the noise level of the air entering the enclosure from the plenum of the invention does not 1. Apparatus for distributing air within a closed volume comprising a hollow distribution tube having an inlet end for receiving air, said tube having a wall defining a plurality of air openings for communicating air from the interior of the tube to the volume, an air-pervious fabric sleeve disposed within said distribution tube and extending from said inlet end to said openings, and means for fixing said sleeve adjacent said inlet end of said distribution tube so that air introduced in said inlet flows through said sleeve to said air openings.

2. The invention of claim 1 wherein said sleeve fixing means comprises a rigid cylinder having an outer surface sized to enter said hollow distribution tube, said cylinder being disposed within said distribution tube at the inlet end thereof and frictionally engaging said sleeve between the outer surface of said cylinder and the inner surface of said distribution tube, said cylinder having an opening therethrough for admitting air interior of said sleeve.

3. The invention of claim 2 wherein said cylinder includes a circular flange at the outer end thereof for limiting movement of said cylinder inward of said distribution tube.

4. The invention of claim 3 in combination with an air delivery tube for delivering air through the opening in said cylinder, said air delivery tube terminating in a fiat face transversely thereof, and means for retaining said air delivery tube so that said flat face bears against said flange to retain said cylinder in place within the inlet end of said air delivery tube.

5. The invention of claim 1 wherein said air distribution has a closed end remote from said inlet end, and means for sup porting said fabric sleeve adjacent said closed end. i

6. The invention of claim 5 wherein said supporting means comprises an 'end portion of said sleeve folded back upon itself adjacent said closed end to form a region within said air dis tribution tube that contains a double thickness of said sleeve.

7. The invention-of claim 1 in combination with a second fabric sleeve disposed in circumscribing relation to the outer surface of said air distribution tube and overlying the air openings in said tube, and means for securing said second sleeve in place.

8. The invention of claim 7 wherein said second sleeve securing means comprises adhesive bearing tape wrapped around the ends of said second sleeve, said tape overlapping the respective ends of said second sleeve and being adhesively joined to the outer surface of said air distribution tube.

9. A method for reducing the noise level of air supplied to the interior of a head enclosure through an opening in a cylindric wall comprising the steps of providing a fabric sleeve having fibers of a diameter less than the opening that are spaced from one another by an amount less than the opening, inserting the sleeve within the cylindric wall so that the fabric overlies the opening, and confining incoming air to the interior of the sleeve.

10. The invention of claim 9 wherein said inserting step comprises providing a relatively rigid rod having an outer dimension less than the inner diameter of the cylindric wall and of the sleeve, inserting the rod in the sleeve, inserting the rod and sleeve into the interior of the cylindric wall, and then removing the rod.

11. The invention of claim 9 wherein air confining step 

1. Apparatus for distributing air within a closed volume comprising a hollow distribution tube having an inlet end for receiving air, said tube having a wall defining a plurality of air openings for communicating air from the interior of the tube to the volume, an air-pervious fabric sleeve disposed within said distribution tube and extending from said inlet end to said openings, and means for fixing said sleeve adjacent said inlet end of said distribution tube so that air introduced in said inlet flows through said sleeve to said air openings.
 2. The invention of claim 1 wherein said sleeve fixing means comprises a rigid cylinder having an outer surface sized to enter said hollow distribution tube, said cylinder being disposed within said distribution tube at the inlet end thereof and frictionally engaging said sleeve between the outer surface of said cylinder and the inner surface of said distribution tube, said cylinder having an opening therethrough for admitting air interior of said sleeve.
 3. The invention of claim 2 wherein said cylinder includes a circular flange at the outer end thereof for limiting movement of said cylinder inward of said distribution tube.
 4. The invention of claim 3 in combination with an air delivery tube for delivering air through the opening in said cylinder, said air delivery tube terminating in a flat face transversely thereof, and means for retaining said air delivery tube so that said flat face bears against said flange to retain said cylinder in place within the inlet end of said air delivery tube.
 5. The invention of claim 1 wherein said air distribution has a closed end remote from said inlet end, and means for supporting said fabric sleeve adjacent said closed end.
 6. The invention of claim 5 wherein said supporting means comprises an end portion of said sleeve folded back upon itself adjacent said closed end to form a region within said air distribution tube that contains a double thickness of said sleeve.
 7. The invention of claim 1 in combination with a second fabric sleeve disposed in circumscribing relation to the outer surface of said air distribution tube and overlying the air openings in said tube, and means for securing said second sleeve in place.
 8. The invention of claim 7 wherein said second sleeve securing means comprises adhesive bearing tape wrapped around the ends of said second sleeve, said tape overlapping the respective ends of said second sleeve and being adhesively joined to the outer surface of said air distribution tube.
 9. A method for reducing the noise level of air supplied to the interior of a head enclosure through an opening in a cylindric wall comprising the steps of providing a fabric sleeve having fibers of a diameter less than the opening that are spaced from one another by an amount less than the opening, inserting the sleeve within the cylindric wall so that the fabric overlies the opening, and confining incoming air to the interior of the sleeve.
 10. The invention of claim 9 wherein said inserting step comprises providing a relatively rigid rod having an outer dimension less than the inner diameter of the cylindric wall and of the sleeve, inserting the rod in the sleeve, inserting the rod and sleeve into the interior of the cylindric wall, and then removing the rod.
 11. The invention of claim 9 wherein air confining step comprises the steps of providing a cylinder having a central opening and an outer diameter slightly smaller than the interior diameter of the cylindric wall, compressing the sleeve between the outer diameter of the cylinder and the interior diameter of the cylindric wall at a site remote from the opening in the cylindric wall, and directing incoming air through the central opening in the cylinder. 